White light indispensable for displays and lighting is generally obtained by combining blue, green and red light emissions according to an addition mixing principle of light. In the displays, in order to efficiently reproduce colors in a wide range on chromaticity coordinates, it is necessary that blue, green and red phosphors have as high emission intensity as possible and good color purity. In general lighting, it becomes necessary that they have high emission efficiency, and that the color of an object irradiated looks like when it is irradiated with natural light, namely, that so-called color rendering properties are high, depending on some applications. In a fluorescent lamp which is typical lighting, an ultraviolet ray having a wavelength of 254 nm caused by discharge of mercury is mainly used as an excitation source, and three kinds of phosphors which emit lights of 450 nm, 540 nm and 610 nm highly sensitive for human eyes are mixed to use, thereby realizing light emission having high color rendering properties. However, when the wavelength of excitation light is in the region from near-ultraviolet light to visible light, no phosphor having high emission efficiency has been developed under the present situation. In particular, to the excitation light in this wavelength range, emission efficiency of the red phosphor is low compared to that of the blue and green phosphors, so that a red phosphor having excellent performance has been desired. When any two or three lights of the above-mentioned 450 nm, 540 nm and 610 nm are obtained from one phosphor, a blending process is simplified compared to mixing of three kinds of phosphors, and stability of performance is expected. However, it had not been realized.
Various phosphors which emit blue, green and red lights in combination with a light source of light emission in the region from near-ultraviolet light to visible light are exemplified in patent document 1. Of these, an alkaline earth metal silicate phosphor is described to emit light in a blue color and a red color. Further, in patent document 2, it is described that a (Ba, Ca, Sr, Mg)—Si—O system activated by Eu2+ emits light at 505 nm in the case of only Ba and Ca, and that emission wavelength shifts to 580 nm when Sr is added. In non-patent document 1, there is a report about (Ba, Ca, Sr)3MgSi2O8:Eu,Mn. Further, in non-patent document 2, it is described that Ba3MgSi2O8:Eu,Mn has emission peaks at 442 nm, 505 nm and 620 nm, and that its crystal structure is merwinite.
[Patent Document 1]
JP-T-2004-505470 (the term JP-T as used herein means a published Japanese translation of a PCT patent application)
[Patent Document 2]
JP-T-2004-501512
[Non-Patent Document 1]
J. Electrochem. Soc., Vol. 115, No. 7, 733-738 (1968)
[Non-Patent Document 2]
Appl. Phys. Lett., Vol. 84, No. 15, 2931-2933 (2004)